1. Field of the Invention
The present invention relates to a hybrid vehicle and a method of controlling the hybrid vehicle. More specifically, the invention relates to a hybrid vehicle that outputs power to a drive shaft linked with drive wheels, and a method of controlling the same.
2. Description of the Prior Art
A proposed hybrid vehicle has an engine, a planetary gear mechanism that includes a carrier connected with a crankshaft of the engine and a ring gear connected with a drive shaft, which is mechanically linked with an axle, a first motor that inputs and outputs power from and to a sun gear of the planetary gear mechanism, a second motor that inputs and outputs power from and to the drive shaft, and a battery that transmits electric power to and from the first motor and the second motor (for example, see Patent Laid-Open Gazette No. 2000-197208).
In this known hybrid vehicle, in response to a driver's step-off action of an accelerator pedal subsequent to the driver's step-on action of the accelerator pedal, the second motor is under regenerative control to output a smoothed driving force, which is obtained by smoothing a driving force demand by the step-off action, to the drive shaft. This relieves the potential shock of torque to the drive shaft, due to a shift from the accelerator-on state to the accelerator-off state. The smoothing operation of the driving force demand corresponding to the driver's step-off action of the accelerator pedal, however, may not immediately change the status of the second motor to the regenerative state but may temporarily keep the second motor in its driving state. This may result in discharge of the battery exceeding its discharge limit in some driving conditions of the first motor.